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Vanadium dioxide (VO2) exhibits an insulator–metal transition (IMT) accompanied with a giant resistance change, which is attractive for the application of devices, such as switching devices. Since the behavior of individual domains determines the total IMT property of the VO2 sample, the steep resistance change from a single domain can be identified and utilized in a sample whose size is as small as the individual domain size. Uniquely, micro-structured VO2 thin films on hexagonal boron nitride (hBN) exhibit step resistance changes owing to the confined metallic domains. In this study, we demonstrated step electrical switching in the two-terminal VO2 sample produced on hBN. Operando structural and electric investigation revealed that the emergence of metallic domains in the micrometer space contributes to the step electric current increase. Our results indicate the use of individual metallic domains in VO2 thin films on hBN in the application of novel devices.

Organic multivalued logic circuits (OMVLs) have drawn tremendous attention due to their high data processability and simple fabrication techniques. However, OMVLs have so far been achieved only on rigid silicon substrates, and this limits their potential for broader applications. In this study, we develop an organic ternary inverter on plastic substrates. The inverters showed well-balanced ternary logic states with high voltage gain and low power consumption. Importantly, the devices exhibited stable operation even after 100 bending cycles, demonstrating high flexibility and reliability. This device has high potential to attain mechanical flexibility and data handling capability at the same time.

We investigate the humidity sensing performance and mechanism of few-layer-thick rhenium disulfide (ReS2) field-effect transistors (FETs) under gate bias operation. Consequently, a negative gate bias exhibits the sensor response, exceeding 90% mainly in the low relative humidity (RH) range. Meanwhile, the threshold voltage change was discovered to be a superior sensing parameter to achieve a broad monitoring of RH range with high response and sensitivity. The approach obtained a practical sensitivity of 0.4 V per 1% RH, which exceed a majority of previous studies with the pristine 2D materials. Besides, our devices display reversible adsorption–desorption and long-term stability operations even after a one-month period. This suggests the sensor capacity to function in real-time applications with a short response and recovery times. These outcomes offer support in the development of adaptable tunable humidity sensors based on ReS2 FETs.

Carbon-based superlattices represent a novel class of quantum metamaterials having promising prospects. Here, we show the first fabrication of folded bilayer-bilayer graphene (fBBLG)/hexagonal boron nitride (hBN) superlattices. In the transport properties at low temperatures, satellite peaks are observed due to the crystallographic angle alignment of fBBLG and hBN. The peculiar resistance peaks appear away from the charge neutrality point and the hBN-induced satellites, which may be signatures of possible competing orders. Our results suggest the emergence of a unique electronic band-structure in the fBBLG, providing a way for investigating the correlated electron phenomena by performing energy-band engineering with superlattice structures.

Two-dimensional ordered arrays of polystyrene microspheres (PSMSs) with a large-scale area were successfully fabricated on a lithographically patterned substrate using a so-called tapered cell. The repetition of the deposition procedure provided the subsequent second array on the first array as a template. Consequently, we succeeded in the fabrication of a Kagome structure on the hexagonally patterned substrate, and evidently observed through the corresponding fluorescence microscopy images that two types of fluorescent PSMSs were, respectively, separately arranged in the dimple and on the terrace. Namely, a potential application of the present method using a patterned substrate would be the step-by-step deposition of microspheres with different refractive indexes, and optoelectronic and magnetic properties.

The optical controllability of single-electron tunnelling using an organic molecular Coulomb island consisting of a porphyrin derivative was examined. A double-barrier tunnelling junction (DBTJ) consisting of a Si/SiO2/molecule/SiO2/Au multilayer exhibited the current?voltage (I?V) characteristics of a Coulomb staircase. Light irradiation was found to induce a reversible change in the threshold voltage of the Coulomb blockade. That is, optical switching of the tunnelling current was achieved under a certain bias voltage. It is believed that the light-induced switching behaviour was due to a change in the charge distribution in the areas near the molecular Coulomb islands. These results demonstrate a potential use for organic molecules in optically functional single-electron devices.

The spontaneous polarization effect of ZnO on the thin film growth of pentacene, which is a typical π conjunction organic semiconductor, was investigated. Pentacene thin films were grown on polar ZnO surfaces by ultraslow organic film physical vapor deposition to obtain layer-by-layer growth. X-ray diffraction measurements revealed that pentacene molecules stand upright on polar ZnO surfaces, and that the films consist of two polymorphs, namely, the thin-film and bulk phases. The thin-film phases of pentacene were observed regardless of the polarity of the ZnO substrate at a thickness of less than six molecular layers. However, pentacene on a Zn-polar ZnO substrate gradually changed to the bulk phase unlike that on an O-polar ZnO substrate. Kelvin probe force microscopy measurements revealed that the surface potential of pentacene becomes more positive with increasing pentacene thickness at less than two molecular layers. The variation in the potential of pentacene on the Zn-polar ZnO substrate was larger than that of pentacene on the O-polar ZnO substrate. These findings indicate that the polarity of the semiconductor can control the growth and electronic state of the inorganic/organic semiconductor interface.

The polarity effects of ZnO on the electronic state of a monolayer pentacene/ZnO interface were investigated by X-ray photoelectron spectroscopy (XPS). XPS revealed that the Zn-polar ZnO (Zn-ZnO) strongly depleted electrons in pentacene at the interface. The O-polar ZnO showed greater electron transfer from ZnO to pentacene than Zn-ZnO. The surface potential of pentacene on ZnO was larger than that of bulk pentacene regardless of the ZnO polarity. These findings indicate that the polarity of ZnO has the potential to control the electronic state of the organic/inorganic semiconductor interface.

We established a process of growing large-scale highly ordered ZnO nanorod arrays on a transparent conductive oxide layer. Nanoimprint lithography was employed specifically to produce large-scale ordered ZnO nanorod arrays. The growth conditions were examined by comparing nanorod growth on different substrates, namely, aluminum-doped zinc oxide (AZO) and indium tin oxide (ITO). Structural characterization revealed that the crystallinity and flatness of the ZnO seed layer were key factors in improving uniformity as regards the diameter, height, and orientation of the ZnO nanorods.

A variety of applications of molecular nanowires is reviewed in the first part of this article. First of all, growth techniques of molecular nanowires are discussed in terms of directed- and self-assemblies. Subsequently, various kinds of functional devices, e.g., field-effect transistors, memory devices, data storage, photo-electric conversion devices, are described. These devices have been proposed by taking advantages of one-dimensional structures and a wide range of molecular functions. In the second part of this article, we demonstrate our recent work. The main purposes are to provide a guideline on molecular design for growing of one-dimensional nanowires and to discuss their optical and electronic properties. A specific stress is laid on multi-level transistor operation as an evidence of effective utilization of one-dimensional nanowires. Although these performances are still preliminary, our results demonstrate a strong possibility of molecular nanowires as components in novel molecular devices.

Nickel oxide nanoplates were continuously synthesized by hydrothermal reaction using a flow-type reactor. The products had a thickness of approximately 10 nm and a lateral size of 100-500 nm. The nanoplates were purified and drop-cast on a bottom-gate substrate and used as the channel material in a field-effect transistor after annealing at 300 degrees C. The I(d)-V(d) profile showed that the NiO nanoplates worked as the p-type semiconductor. This result suggests that various electronic devices can be prepared using metal oxide nanomaterials, which exhibit various properties including magnetism, ferroelectronics and catalysis as well as stability and safety in air and water.

Lattice strains near the Si/NiSi2interface and their effects on electron energy-levels of Si were investigated via experimental and theoretical approaches. For highly spatially resolved analysis, electron nanoprobe techniques were employed: convergent beam electron diffraction (CBED) for lattice strain and electron energy-loss spectroscopy (EELS) for the electron energy-levels. Additionally, a theoretical analysis based on the density-functional theory (DFT) was performed to explain the experimental results. The actual distribution of the lattice strains was complicated; both tensile and compressive strains were found to coexist near the interface. Shifts in the SiL23-edge of the EEL spectra were found to be induced by the lattice strain. Finally, we described the “distribution of the electron energy-levels” as the strain distribution around the interface in a submicron region.

Lattice strain distribution was measured in Si substrates near NiSi2 islands. Using the convergent beam electron diffraction (CBED) technique, quantitative and highly spatially resolved evaluations were carried out. Variations in the CBED patterns were found to be due to a combination of stress components with different orientations and magnitude. As a result, it was revealed that, in addition to normal stress components, singular stress with characteristic orientation or extremely high strain concentration was observed, especially near the NiSi2 island corner. This actual strain distribution was considered to be highly influenced by the shape, size and orientation of the NiSi2 island on Si substrates.

The crystal growth of Si in SiO2/a-Si/SiO2 layered structures is examined by high resolution transmission electron microscopy. In a thin a-Si layer (10 nm), crystal growth halts with the crystallite size roughly equal to the layer thickness. In a thick layer (50 nm), crystal growth continues beyond the layer thickness. An expression for this halt in growth is derived from the free energy change. The halt in growth of Si crystallites suggests that the a-Si/SiO2 interface and the a-Si/c-Si interface are more stable than the c-Si/SiO2 interface.

Lattice strain distribution was measured in Si (111) substrates near NiSi2 islands. Quantitative measurements with high spacial resolution were performed using convergent beam electron diffraction (CBED). Distorted and lower-symmetry CBED patterns were observed up to 2.0 µm from NiSi2 islands. We show that these CBED patterns can be accounted for by a combination of stress components with different orientations. Stresses were found to be tensile perpendicular to NiSi2 island edges and compressive parallel to them. In addition, another stress component which had a characteristic orientation was detectable within 0.5 µm of NiSi2 island edges.